The present invention relates to an apparatus and method for recorrugating the ends of a helically corrugated pipe in which damage to the ends of the pipe as it is being recorrugated is minimized.
It has long been known that corrugating the side walls of a steel pipe greatly increases its strength. Because of the manner in which such corrugations are formed in the side walls of the pipe, most pipe is helically corrugated, i.e., the corrugations run in a helical fashion along the side walls of the pipe. However, difficulties have been encountered in making water tight connections at the junction between such helically corrguated pipe sections. As a result of these problems, it has been found best to recorrugate the ends of such pipe so that the ends have annular corrugations to facilitate the making of watertight connections between adjacent sections of pipe.
Machines have been developed for recorrugating the ends of helically corrugated pipe so that the corrugations are annular. However, in such machines, it has been found that the helical corrugations act as threads to move the pipe in the directions of the corrugations and the pipe is not properly recorrugated. To counteract this effect, it has been found necessary to abut the ends of the pipe against a stationary thrust plate. However, the force exerted by the pipe on the thrust plate is relatively large, and the friction between the pipe and the thrust plate damages the ends of the pipe. In addition, it has been found that recorrugating both ends of the pipe in a single step doubles the force on the thrust plate and compounds the problem. Accordingly, the ends of the pipe must be recorrugated one at a time, greatly complicating the recorrugating procedure, and damage to the the pipe remains excessive.
The difficulties in recorrugating the ends of the helically corrugated pipe and the damage caused to such pipe in the recorrugating procedure necessarily degrades the quality of any junction which can be formed between adjacent pipe sections. As a result, the use of such recorrugated pipe is often looked on with disfavor where junctions are required between adjacent sections of pipe. In such situations concrete pipe is ordinarily used in place of recorrugated steel pipe even though the steel pipe may possess other advantages over such concrete pipe.